

3. There was no difference in the 

 average number of return 

 strokes per discrete discharge 

 (4.1 unseeded vs. 4.0 seeded). 



The average duration of dis- 

 crete discharges (period be- 

 tween first and last return 

 stroke) decreased from 235 mil- 

 liseconds for unseeded storms 

 to 182 milliseconds for seeded 

 storms. 



5. The average duration of con- 

 tinuing current in hybrid dis- 



charges decreased from 187 

 milliseconds for unseeded 

 storms to 115 milliseconds for 

 seeded storms. 



Inferences 



The results from the seeding ex- 

 periments to date strongly suggest 

 that lightning frequency and char- 

 acteristics are modified by massive 

 seeding with silver iodide freezing 

 nuclei. While the physical mechanism 

 by which massive seeding modifies 

 lightning activity is not fully under- 

 stood, there is evidence that the 



basic charging processes are altered 

 by the seeding. Further, it has been 

 established on the basis of direct 

 measurements that hybrid discharges 

 (lightning strokes that contain a con- 

 tinuing current) may be responsible 

 for most lightning-caused forest fires. 

 Thus, a substantial reduction in the 

 duration of the continuing-current 

 portion of the hybrid discharge may 

 have a large effect on the ability of 

 an individual discharge to ignite fuels 

 or to cause substantial damage. This 

 change in the nature of the discharge 

 may be more important than a change 

 in the total amount of lightning that 

 is produced by the storms. 



161 



